This invention relates to torque control in automotive permanent magnet (PM) brushless electric motors.
It is known in the art of permanent magnet brushless electric motors to control torque by aligning phase currents with back-emf. The torque delivered by the electric motor is then directly proportional to the phase current and is therefore easily controlled by simply controlling the aligned phase currents. This is commonly referred to as xe2x80x9ccurrent mode control.xe2x80x9d The drawback is that current sensors are required to determine what the currents are. The sensors necessarily have a finite, though small, dc voltage drops that induce torque ripple into the motor.
An exemplary embodiment is a method of controlling torque in electric motors that is analogous to traditional current mode control methods, but which requires no current sensors to determine what the current is in any particular phase. Instead, phase current information is calculated from knowledge of the rotor""s position and rate of rotation. The information is used to calculate a required voltage and electrical angle offset needed to obtain a user-specified torque. The calculated voltage and offset is added to the input power of the electric motor by known means, usually an inverter.